Project Information

Summary:

Successfully no-till interseeding yellow-flowered alfalfa into crested wheatgrass stands is dependent on good environmental conditions and management practices. Seeding date, sod suppression, and seeding rate can affect initial establishment of yellow-flowered alfalfa. However, environmental conditions will often have a greater influence on initial establishment than management practices. Interseeding alfalfa in semiarid regions is risky because of erratic precipitation, grasshoppers, and other factors. Interseeding techniques such as herbicide sod suppression and high seeding rates can be costly and may not always be successful. Interseeding techniques that are low cost will minimize financial risk if establishment is poor.

Introduction:

Crested wheatgrass stands are prevalent in the Northern Great Plains and Intermountain West. The grass is valuable for early spring grazing, stabilizing soil, and suppressing noxious weeds (Asay and Jensen 1996). However, crested wheatgrass was often planted in monocultures (Asay and Jensen 1996). Interseeding yellow-flowered alfalfa would increase forage production, forage quality, and diversity of crested wheatgrass stands in semiarid regions.

Interseeding is a method for introducing desirable plant species to a plant community using minimal or partial soil disturbance. Interseeding is desirable when the risk of erosion is high, complete seedbed preparation is not practical, and/or the goal is to modify the existing plant community (Vallentine 1980). Adequate and timely precipitation is necessary for interseeding to be successful (Rumbaugh and Thorn 1965). Reducing grass competition, proper seeding depth, and good seed-to-soil contact improve establishment (Rohweder and Albrecht 1995).

Early spring (April) is the best time to interseed alfalfa in the Northern Great Plains (Twidwell et al. 1993). However, alfalfa has also been interseeded in late summer (late August) and autumn (October-November) (Rumbaugh and Thorn 1965).

Physical and/or chemical sod suppression can be used to reduce competition from the existing vegetation when interseeding alfalfa. Physical sod suppression techniques include tillage, grazing, mowing (clipping), and burning. Historically, interseeding in semiarid regions utilized strip-tillage on wide rows to create furrows in the sod (Vallentine 1980). Chemical sod suppression techniques include broadcast or band herbicide application. Banding herbicide has been recommended for introducing legumes into desirable grass stands (Hall and Vough 2007).

Seeding rates have generally been low for interseeding alfalfa in semiarid grazing lands. Seeding rates from 1.12 to 2.24 kg Pure Live Seed (PLS) per hectare have been suggested (Rumbaugh et al. 1982). Wide rows (61 to 122 cm) increase the concentration of seed within a row when seeding rates are low.

Project Objectives:

Determine interseeding techniques that will provide the highest probability of success with the fewest resources (financial, time, and labor).

Research

Materials and methods:

The study was initiated in August 2008 at four locations in the Northern Great Plains. The Northern Great Plains is characterized by a semiarid climate. About 75% of the annual precipitation occurs from April through September.

Three factors were evaluated in a split-plot experiment design at each location. Factors were seeding date (late summer and spring), sod suppression (clethodim herbicide and untreated control), and seeding rate (0.56, 1.12, 3.36, 5.60, and 7.84 kg PLS ha-1). Late summer seedings were conducted in late August, while spring seedings were conducted the following May.

Inoculated ‘Falcata’ alfalfa (Wind River Seed, Manderson, WY) was no-till interseeded using a plot drill with John Deere 750 single-disk openers (Deere &amp; Company, Moline, IL). Seed was routed to two openers to achieve a row spacing of 127 cm. Clethodim herbicide was band applied (1 L per treated ha) onto rows of alfalfa seeded in the spring and the previous summer. Clethodim, a grass selective herbicide, allowed application in late May if alfalfa had emerged. Band width was 40.6 cm.

Successful initial establishment of yellow-flowered alfalfa in crested wheatgrass stands is dependent on favorable growing conditions. Environmental conditions appear to have a greater influence on interseeded alfalfa establishment than management. However, management does have an important role in establishment. The following information is provided to show how various factors play a role in initial alfalfa establishment.

Precipitation. Adequate and timely precipitation is necessary during initial establishment. Initial establishment was poor at locations where growing season precipitation was below normal. High mortality of alfalfa seedlings will occur if rains are followed by long dry periods. Seeds may germinate and emerge when growing conditions are favorable. However, establishment is not guaranteed unless environmental conditions remain favorable.

Most crested wheatgrass pastures are not irrigated in the Northern Great Plains. Therefore, producers do not have the ability to provide moisture to alfalfa seedlings if conditions are dry. Establishment of interseeded alfalfa in crested wheatgrass is risky when precipitation is erratic. Established crested wheatgrass increases risk because of interspecific competition with the small alfalfa seedlings.

Seeding rate. Five seeding rates ranging from low (0.56 kg PLS ha-1) to high (7.84 kg PLS ha-1) were researched at each location. Generally, seedling frequency increased as seeding rate increased at all locations. However, the response to seeding rate was dependent on environmental conditions, particularly precipitation. In July 2009 and 2010, mean seedling frequency was below 15% for all seeding rates at Fruitdale. At Hettinger in July 2009, mean seedling frequency was greater than 45% for all seeding rates. Under good growing conditions, mean seedling frequency approached 100% at high seeding rates.

Good emergence at high seeding rates (5.60 and 7.84 kg PLS ha-1) initially resulted in excessively thick stands when seeded in 127-cm wide rows. However, most of the alfalfa seeds planted will not establish into mature plants. Competition, moisture stress, and other factors will cause seedling mortality through time. Seedling frequency measurements in the year after establishment for Experiment I revealed that seedling frequency had declined at all locations. Declining seedling frequency through time is a possible trend resulting from seedling mortality.

The desired final plant stand is 3 to 6 mature alfalfa plants per meter of row. Seedling frequencies ? 50% will achieve this stand if establishment is successful. However, seedling frequency is dynamic in the year of establishment. Initial stands may look promising, but poor environmental conditions later in the growing season can be detrimental. Excellent stands of spring seeded alfalfa were observed at Fruitdale in June 2010. However, grasshoppers had consumed the alfalfa by July 2010 when frequency measurements were taken.

Seeding date. Alfalfa interseeded in late summer 2008 (Experiment I) at Newcastle established in September because of good growing conditions and adequate establishment time. At Buffalo and Hettinger in Experiment I, late summer seeded alfalfa did not germinate until the following spring. Dry conditions in autumn most likely prevented germination.

Initial establishment of late summer seeded alfalfa in autumn is possible if adequate growing conditions exist. Killing frosts in autumn are a risk and could result in poor stands if alfalfa is not fully established. Interseeding alfalfa during the dormant season (late October or November) would eliminate the risk of autumn frosts killing emerged alfalfa. However, spring killing frosts are an issue if seed lays dormant through winter and emerges too early in the spring. Adequate residue cover would keep soils cooler in the early spring and may prevent early germination.

Late summer seeded alfalfa was significantly (P < 0.05) taller than spring seeded alfalfa at Newcastle, Buffalo, and Hettinger in both experiments. Late summer seeded alfalfa was already growing before alfalfa was planted in mid May.

Interseeding alfalfa in early spring (April) is the recommended practice in the Northern Great Plains. Good initial alfalfa stands can result from interseedings in mid May if growing conditions are favorable. However, interseeding alfalfa in mid May is more risky than April. Crested wheatgrass competition is higher in May than in April. Growing conditions also become less favorable for establishment in June and July. Interseeding alfalfa at Fruitdale in late April 2010 would have provided more establishment time before grasshoppers consumed the stand. Critical establishment time may be lost by delaying interseeding into mid May.

Clethodim herbicide significantly (P < 0.05) increased below canopy PAR levels at each location in both experiments. Seedling frequency and height can also be significantly increased by clethodim application. However, growing conditions (e.g. moisture) appear to have a greater influence on alfalfa establishment than clethodim application. Alfalfa establishment may not be considerably improved in certain situations when clethodim is applied. Increased light levels do not provide much benefit to seedlings if moisture is lacking. Grasshoppers will also consume alfalfa stands whether clethodim is applied or not.

Alfalfa can initially establish in crested wheatgrass without clethodim application if growing conditions are favorable. Low crested wheatgrass cover is also beneficial for establishment. Lack of grazing for more than one growing season and high moisture may result in thick, trashy stands. Thick vigorous growth and old residue comprise these stands. Thick, trashy stands may not be an ideal environment for establishing alfalfa, particularly if grass is not suppressed using herbicide.

Heavy sheep grazing at Fruitdale in spring 2010 was found to reduce surface plant material of a thick, trashy stand. Conditions were dry when the stand was grazed. Heavy grazing weakened crested wheatgrass and animal impact reduced standing residue to a surface mulch. Alfalfa interseeded into this environment in mid May 2010 looked excellent until grasshoppers consumed the stand. Crested wheatgrass remained short and thin for the remainder of the growing season.

Project Outcomes

Project outcomes:

Yellow-flowered alfalfa has high potential to improve forage production and quality of crested wheatgrass stands. In addition, plant diversity and wildlife habitat would also be improved by the inclusion of alfalfa. Rising input costs in production agriculture make generating a profit increasingly difficult. Reducing external inputs while maintaining or increasing production is a good way to increase net profits. Dryland beef production can be doubled by adding alfalfa to the grassland ecosystem (Lorenz et al. 1982).

Persistence of yellow-flowered alfalfa in crested wheatgrass stands will ensure that production is maintained through time. Yellow-flowered alfalfa can initially establish in crested wheatgrass stands. However, it is difficult to determine establishment success or failure in just one or two years after interseeding. Development of interseeded yellow-flowered alfalfa into productive stands is slow and may take as many as five years (Smith 1997). Competition from crested wheatgrass will cause development to be slow. Grazing management and growing conditions during these five years will also affect stands.

Interseeding yellow-flowered alfalfa into crested wheatgrass stands would improve many hectares of grazing land in the Northern Great Plains. The project will only have an impact if initially established stands develop into productive stands in the next few years.

Economic Analysis

As expected, input costs rose as seeding rate was increased and herbicide was used to suppress the grass. Broadcasting clethodim was not studied in this research. Banding herbicide is considerably less expensive than broadcast application since only 1/3 of an area was actually treated. Less herbicide and carrier (water) is needed when herbicide is band applied.

Clethodim is a grass selective herbicide and is more expensive than herbicides such as glyphosate. However, clethodim provided the flexibility needed in this study to suppress grass after the alfalfa was interseeded. Results of this study revealed that clethodim herbicide may or may not benefit initial establishment. Environmental conditions during establishment had a major influence on the effect of clethodim herbicide.

Some people expressed concern that most ranchers would not be willing to use herbicide for sod suppression when interseeding. The son of a rancher from central South Dakota was one of those people. Less labor, time, equipment, and money is required when herbicide is not used. Many producers do not have the equipment to apply herbicide, particularly in bands. Herbicide must also be applied when weather conditions are adequate and grass growth stage is suitable for effective control.

Using a herbicide for sod suppression is a decision best made by the producer. Physical sod suppression techniques such as grazing, mowing, and/or strip-tillage may be more appealing to some producers. Physical sod suppression techniques are often cheaper and more convenient to use than chemical sod suppression. Heavy spring grazing before interseeding at Fruitdale in spring 2010 was found to be beneficial in suppressing crested wheatgrass.

Interseeding is a high risk operation because of the large influence of environmental factors in determining success or failure. The traditional approach of using strip-tillage and low seeding rates to interseed alfalfa was probably a fairly low cost seeding operation. No-till interseeding has potential, but low cost sod suppression methods that complement it would be the most economical to use. Producers may be more willing to use higher seeding rates rather than herbicide to increase the chances of successful establishment.

Failures may occur when using any technique. However, the financial loss from a failed interseeding may be less if low cost techniques are used.

Farmer Adoption

Interest in interseeding yellow-flowered alfalfa in crested wheatgrass has been expressed by producers and government agency personnel. However, the practice has not been widely adopted by producers. A news release about the project was published in a variety of regional agricultural publications (Dakota Farmer, Farm Forum, and Tri-State Livestock News) in 2010. Producers and other people who read these publications are aware of the project.

Recommendations to producers are based on the results and observations from this project:

•Interseeding in April rather than mid May will provide more establishment time when conditions are usually most favorable.

•Suppression of crested wheatgrass with herbicides, grazing, or other methods is beneficial.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.

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